This is certainly easier than the last question! Who is deliciously villainous enough to qualify for this honour?
Gul Dukat from DS9 springs to mind. He was always scheming and plotting, doing everything he could to elevate himself. He wanted his people to be strong and if that meant placing them in the clutches of a tyrannical regime then so be it.
Dukat is winner here, but an honourable mention goes to Ward from Agents of Shield. He was a very different villain, at first motivated by misplaced loyalty, and then revenge. He was single-minded and ruthless, something that made him almost unstoppable at times.